Ignition coil construction



Oct. 8, 1963 T. F. CARMICHAEL 3,106,655

IGNITION COIL CONSTRUCTION Filed March 12, 1959 3 Sheets-Sheet l j/ I J; 3% INVENTOR. I J4 4 7/;477/4: )iCarzzzz/Zae/ 1 Oct. 8, 1963 'r. F. CARMICHAEL IGNITION COIL CONSTRUCTION 3 Sheets-Sheet 2 Filed March 12, 1959 I N VEN TOR. 6' 47271 ZZ/Zd? mwvI/ 773 774.; /F BY Oct. 8, 1963 T. F. CARMICHAEL IGNITION COIL CONSTRUCTION 5 Sheets-Sheet 3 Filed March 12, 1959 IN V EN T 0R. 7/?477745 id'drwzi/gxcz 3,106,655 IGNITION COIL CONSTRUCTIGN Thomas F. Carmichael, Plymouth, Micln, assignor to Syncro Corporation, Oxford, Mich., a corporation of Michigan Filed Mar. 12, 1959, Ser. No. 799,049 3 Claims. (Cl. 310-70) This invention relates to ignition coil constructions, and more particularly to the constructions of magnetos and battery-operated coils such as are used for ignition purposes. This application is a continuation-in-part of application Serial No. 781,691, tiled December 19, 1958 now abandoned, entitled Magneto Construction.

It is an object of the invention to provide a novel and improved ignition coil construction which eliminates the need for a separate capacitor in parallel with the breaker points and substantially reduces the fabricating cost of the coil assembly.

It is another object to provide an improved ignition coil construction of this character which is efiicient in eliminating sparking across the breaker points, acts to increase output voltage, and serves to inhibit minor sparking tendencies upon increase in rotational speed of a magneto.

It is also an object to provide an improved ignition coil construction of this nature which is of versatile construction to suit various requirements and may be incorporated in a conventional generator-magneto construction.

It is a further object to provide an improved ignition coil of this type which is of relatively small diameter for a given output, thus greatly reducing the amount of copper wire needed for the secondary turns and resulting in a substantial cost saving.

Other objects, features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIGURE 1 is an elevational view, partly in cross section, of one embodiment of the invention of a magneto type incorporated in an internal combustion engine and flywheel assembly;

FIGURE 2 is a plan view of the structure in FIG- URE 1, showing the breaker points and a portion of the flywheel;

FIGURE 3 is an enlarged fragmentary cross-sectional view of portions of the magneto coil showing several turns of the primary winding as well as the connection between the two foil strips; v

FIGURE 4 is a schematic representation of the coil and the circuit in which it is connected;

FIGURE 5 is an elevational view of a modified form of the invention incorporated in a generator-magneto construction;

FIGURE 6 is an end elevational view of the primary and secondary windings of the magneto coil of FIGURE 5, taken along the line 6-6 thereof;

[FIGURE 7 is an exploded perspective view of another form of the invention for use in battery ignition systems;

FIGURE 8 is a circuit diagram of a battery ignition system using the coil of FIGURE 7; and

FIGURE 9 is a circuit diagram of a further modification of the invention in which a ground connection is made at the juncture of the first and second primary coil strips.

In general terms, each of the illustrated embodiments of the invention comprises an ignition coil construction having a primary coil which is fabricated of a plurality of flat strips of an electrically conductive material such as aluminum. These strips are coiled in overlapping relation around the core, strips of dielectric material being interleaved between the conductive strips. The result is a primary coil which exhibits capacitative as well as inductive qualities, so that sparking at the breaker points, which would ordinarily occurwithout a separate capacitor in parallel with the primary coil, is eliminated. The secondary coil is fabricated of copper wire turns surrounding the primary in a conventional manner. Because of the novel primary coil construction, substantial cost savings in secondary coil material are obtained, and the inductive connection between the primary and secondary is improved.

FIGURES l4 show a suitable form of the invention comprising a magneto coil generally indicated at 11 which is incorporated in an assembly including an internal combustion engine shown in dot-dash lines at 12. This engine is illustrated as having a vertically disposed crankshaft 13 projecting from the upper end of the motor casing, with a flywheel shown in dot-dash lines at 14 being secured to the upper end of the crankshaft. Motor 12 may be used for example in such installations as lawn mowers or similar equipment. Flywheel 14 may have an annular portion within which is secured a permanent magnet 15, as seen in FIGURE 2, so that magnet 15 rotates with the flywheel about the axis of shaft 13.

A magneto supporting bracket 16 is secured to the top of engine 12 within the confines of flywheel 14. This bracket is provided with a pair of slotted portions 17 for the reception of bolts 18 which secure it to the engine. A laminated core 19 is secured to one side of bracket 16 by fasteners 21, this core being of generally E-shaped construction and having outer poles 22 and a central pole 23, the outer surface of these poles being of arcuate shape to accommodate flywheel 14. Also formed on bracket 16 is a housing 24 which surrounds an aperture 25' provided in bracket 16 for shaft 13, the latter extending through the housing. Housing 24 has a cover plate (not shown) and is adapted to enclose a stationary breaker point 26 and a movable breaker point 27, the latter being carried by a rocking member 23 pivoted to bracket 16. Breaker point 27 and its supporting member 28 are urged against breaker point 26 by a leaf spring 29 which is secured to housing 24. A cam 30 is secured to shaft 13 and serves to rock member-28 when the engine is running to open and close the breaker points.

Pole 23 of core 19 carries the magneto coil assembly generally indicated at 11. Theconstruction of this coil assembly is best seen in FIGURES 3 and 4. The assembly comprises a primary winding generally indicated at 31 in FIGURE 3 and a secondary winding 32. As in conventional magneto constructions, the secondary wind ing consists of many turns of fine copper wire, this winding surrounding primary winding 31 which is adjacent pole 23.

Primary winding 31 comprises two flat strips 33 and 34 of electrically conductive material which are wound in the same sense and in overlapping relation around pole 23 and which are separated by two fiat strips 35 and 36 of dielectric material. As seen best in FIGURE 3, which has exaggerated dimensions, the outer end of strip 33 is connected to the inner end of strip 34 by lateral tabs 37 and 38 formed on the two strips, these tabs being brazed together. connected in magnetically aiding relation when wound on pole 23. The inner end of strip 33 is connected to ground by a connection 39 as seen in FIGURE 4, While the outer end of strip 34 is connected to stationary breaker point 23 by a wire 40 through terminal 41 on housing 24 and spring 29. g

In a suitable construction described for illustrative purposes, primary winding 31 was fabricated of two parallel anodized aluminum foil strips each of which was The strips are thus series seven-eighths of an inch wide and 0.0005 inch thick. Separators 35 and 36 were fabricated of kraft paper one inch wide and 0.0003 inch thick, the extra width preventing inadvertent contacting of adjacent foil edges. After securing wires 39 and 40 to the foils, the strips were wound on a tubular paper support 42 and tabs 37 and 38 secured together. The foil strips each had 75 turns, so that the total number of turns in the primary was 150. The secondary was wound separately of 10,000 turns of No. 43 gauge copper wire and a lead 43 secured to one end of the secondary for connection to the spark gap, the other end of the secondary being grounded by connection to wire 39. After placing the primary and secondary coils in a cup-shaped plastic enclosure 44, the assembly was impregnated with a potting material of high dielectric strength to hold the coils in place and provide mechanical strength as well as moisture resistance. Enclosure 44 was provided with an enlargement 45 for the reception of high voltage lead 43, and a connection 46 was provided within the enclosure for the grounded end of the secondary leading to grounded tab 47 of foil 33.

In operation, electrical currents are induced in primary coil 31 as magnet passes poles 22 and 23 on core 19. As breaker points 26 and 27 are opened, the primary coil current will be interrupted, and the rapid movement of the magnetic lines of force across secondary winding 32 will induce a momentarily high voltage in this winding, thus making a high voltage available at spark gap 48 in FIGURE 4.

It has been found that the novel primary coil construction provides a capacitative effect which will reduce or eliminate sparking at the breaker points when they are opened. As is will known, such sparking is ordinarily produced by self induction in the primary circuit, and conventional ignition coil constructions provide a separate and sometimes costly capacitor connected to ground and in parallel with the primary coil. Because of the capacitative effect of the novel primary coil construction, the use of such a separate capacitor has been found to be completely unnecessary.

In use, it has also been noted that upon an increase in rotational speed of shaft 13, any minor sparking occurring at breaker points 26 and 27 tended to decrease. With a conventionally wound magneto coil assembly using a separate capacitor, the opposite condition oc curred, that is, minor sparking tended to increase with an increase in rotational speed. Another advantage of the novel ignition coil construction over conventional constructions using separate capacitors appears to be an improvement in electrical efiiciency. This is thought to be at least partially due to the fact that electrical energy which would ordinarily be transmitted back and forth between lumped components (capacitor and primary coil) in a conventional ignition coil assembly need not be so transmitted in the novel coil, since the inductive and capacitative elements of the circuit are integrally formed.

Important advantages of the novel coil construction of this invention are also obtained by virtue of substantial reductions in manufacturing costs and in compactness of assembly, that is, in preventing an excessively large coil assembly diameter. The fact that each of the turns of the primary coil extends in width across all the turns of the secondary coil results in a much closer coupling between the primary and secondary than would otherwise be the case, so that the output from the secondary may be made sufficiently high with relatively smaller dimensions of the parts. Moreover, each turn of the primary will have a portion closely adjacent the air gap between pole 23 and magnet 15. This will in crease the magnetomotive force imposed on the primary by the moving magnet, and will also serve to more ethciently charge the capacitative elements which make up the primary winding. In conventional wire-wound primary constructions, many turns will be a substantial distance from the air gap. As another factor, the series aiding relation of the two strips comprising the primary coil aids in inhibiting large transient voltages from being produced each time the breaker points are opened, even though a relatively large distributed capacitance is maintained. This lack of high transient voltages permits the use of thinner separator strips between the foils, resulting in a substantially smaller total diameter of the primary coil. This in turn saves considerable length and weight of copper Wire in the secondary for any given number of turns. Since the cost of the secondary coil constitutes the greatest portion of the total material cost in the ignition coil, this reduction in the necessary amount of copper wire results in a very substantial cost saving.

Another way in which the novel construction of this invention reduces the diameter of the secondary coil, and thus the material cost, is found in the fact that the crosssectional areas of the primary turns can be maintained below the wire sizes which would ordinarily be necessary to prevent undue temperature rises. For example, if the primary turns are fabricated of aluminum foil (which would ordinarily have to be of larger cross-sectional area than copper because of the higher resistivity of aluminum) it has been found that the distributed capacitance existing between the overlapping foils increases the effective conductivity of the series-connected foils, so that actually the cross-sectional area of the aluminum foils can be made less than that which would ordinarily be needed if copper wire were used for the primary. The reduction in thickness of the foils will result in a smaller diameter for the primary coil and hence a smaller secondary coil diameter.

The use of anodized aluminum foil strips for the primary coil has been found to produce advantageous results, especially when combined with an impregnant of high dielectric properties. These elements in the con struction help to create a relatively high capacitance for a given number of turns in the primary.

It should also be observed that the novel primary winding construction is quite flexible to suit individual requirements, in that the relative amounts of capacitance and inductance could be varied by using proper lengths and other dimensions of foils 33 and 34.

In some cases, it has been found that by selecting a relatively low natural resonant frequency for the primary circuit, and therefore for the coil assembly, starting of an engine can be greatly facilitated, and engine performance made smoother at low or idling speeds. An advantage of the novel ignition coil construction of this invention is that it enables the natural resonant frequency to be chosen at a lower value without unduly increasing the cost or size of the unit or detracting from the effect of the capacitance in quenching the breaker points at all running speeds.

FIGURES 5 and 6 illustrate a generator-magneto construction generally indicated at 111 which incorporates the constructional principles of the invention. The generator-magneto is of an inductor type and comprises a central shaft 112 rotatably driven by means (not shown) such as an automobile engine, and an annular magnet frame shown in dot-dash lines at 113. The magnet frame is secured to shaft 112 and surrounds a stationary coil and core assembly generally indicated at 114. Frame 113 carries one or more permanent magnets 115 having an arcuate shoe 116 extending on opposite sides thereof. Coil and core assembly 114 has a number of load or generator coils 117, 118 and 119 on appropriate core poles. Since these load coils in themselves form no part of the present invention, their construction and interrelationship need not be described in detail. As an example of such a construction, reference is made to application Serial No. 628,439, filed December 14, 1956, by the present applicant and entitled Generator System."

A bracket 121 is secured to assembly 114 and carries a stationary breaker point 122 which is grounded, as well as a movable breaker point 123 carried by a member 124 which is pivoted at 125 on bracket 121. Arm 124 is engageable with a cam 126 mounted on shaft 12, and a leaf stpring 127 is secured to bracket 121 and urges arm 124 in a direction such that breaker point 123 is in engagement with breaker point 122.

A magneto ignition coil generally indicated at 128 is mounted on a pole 129 of assembly 114. The construction of this ignition coil assembly is similar to that of the previous embodiment, and need not be described in detail. The assembly comprises a primary winding 131 and a secondary winding 132. The primary winding is fabricated of two electrical conductive foil strips wound in overlapping relation and in the same sense around pole 129, these foils being separated by dielectric material. The secondary winding consists of a much larger number of fine copper wire turns. The connections of the primary and secondary coils will be the same as those described with respect to the previous embodiment.

In operation of the embodiment of FIGURES and 6, rotation of magnet frame 113 will induce currents in the primary coil, breaking of the primary circuit by breaker points 122 and 123 inducing a relatively high voltage in the secondary coil. The capacitative eil'cct of the primary turns, and the advantages in construction and operation of the unit, will be similar to that described previously.

FIGURES 7 and 8 show another embodiment of the novel ignition coil especially adapted for use in conjunction with a battery ignition system such as is used for automotive vehicles. The coil assembly is generally indicated at 211 and comprises a housing 212 of tubular shape, a primary Winding generally indicated at 213, a secondary winding 214, a laminated core 215 and a cap 216. Primary winding 213 comprises a first foil strip 217 and a second foil strip 218 wound in overlapping relation and disposed Within casing 212, it being understood that some conventional components such as insulative elements Within the casing are omitted from the drawing for purposes of simplicity. A first pair of insulative sheets 219 and a second pair of insulative sheets 221 are wound with strips 217 and 218, together with an insulative outer wrap 222. The outer end of the first foil 217 has a laterally extending tab 223 which is electrically joined with a tab 224 on the inner end of foil 218. The inner end of foil 217 has a tab 225 which is connected to a positive terminal 226 mounted on cap 216 during final assembly. The outer end of foil 218 has a lateral tab 227 which is similarly connected to the negative terminal 228 carried by cap 216.

Secondary coil 214 is disposed within primary coil 213 and comprises a large number of turns of fine copper wire. The inside lead 229 of coil 214 is connected to a high tension lead 230 extending from the central portion of cap 216, and the outer lead 231 of coil 214 is connected to ground by any appropriate means. Core 215 is disposed within coil 214 and comprises laminated sheets of steel or other magnetizable material.

FIGURE 8 is a simplified circuit diagram showing the manner in which the ignition coil of FIGURE 7 may be connected in a battery ignition system. A battery 232 is connected through an ignition switch 233 with the positive terminal 226 of ignition coil 211. The negative terminal 227 is connected through a breaker switch 234 in the distributor to ground. High tension lead 229 is connected to the distributor which in turn connects this lead to spark plugs 235.

The operation of the embodiment of FIGURES 7 and 8 will be similar to that described above with respect to the previous embodiment. Upon closure of the ignition switch and operation of the engine, breaker switch 234 will periodically open and close, causing the primary coil to induce a voltage in the secondary coil. The advan- Y 6 tages of the novel primary coil construction described above will of course be applicable to this embodiment of the invention.

FIGURE 9 is a circuit diagram showing a modified form of the invention which is basically similar to those previously described but in which the ground connection is made at the juncture of the first and second primary coil strips. In this figure, the ignition coil assembly is generally indicated at 301 and comprises a primary coil generally indicated at 302 and a secondary coil 303. The primary coil comprises a pair of electrically conductive foil strips 304 and 305, the foils being wound and insulated from each other as in the previous embodiment.

' One end of strip 304 is connected through an ignition conventional fashion with switch 306 to a battery 307, and the other end is connected by means 308 to the first end of foil 305, so that these two foils are wound in series aiding relation around core 369. One end of secondary coil 303, which is wound in many turns of copper wire, is connected to distributor arm 311, while the other end is grounded.

In this embodiment of the invention, a ground connection 312 through breaker points 313 is provided for the juncture 398 between foils 364 and 305. The free end of foil 365, which would normally be grounded as shown in the other embodiments, is left unconnected to ground. Tests have shown that an ignition coil wound and connected in accordance with the circuit diagram of FIGURE 9 achieves the advantageous and desirable results discussed above with respect to the other embodiments. In other words, this type of construction eliminates the need for a separate capacitor in parallel with the breaker points, is efiicient in eliminating breaker point sparking and acts to increase output voltage. An advantage accruing from the circuit shown in FIGURE 9 is that foil 335 does not carry full primary coil current, although it does cooperate with foil 304 in producing the capacitative efiect of primary coil 302. The primary coil circuit as a whole thus exhibits less total resistance. Since foil 305 does not carry this current, it may be made relatively thin, the smaller cross section having no resistance effect during operation. This in turn would result in a smaller total diameter of the ignition coil with a consequent space saving. The arrangement of FIG- URE 9 could also be used in a magneto ignition coil instead of with a battery power supply as shown. 7

While it will be apparent that the embodiments of the invention herein disclosed are well calculated to fulfill the objects of the invention, it Will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope or fair meaning of the subjoined claims.

What is claimed is:

1. In an ignition coil for use in a magneto assembly of the type having relatively rotatable core and magnetic field structures with an air gap therebetween and means for periodically opening a primary Winding circuit, a primary winding comprising at least two elongated flat strips of electrically conductive material Wound in overlapping relation on a portion of said core structure, dielectric material separating said strips, each turn of said primary Winding having a portion positionable closely adjacent said air gap, means connecting said strips in series aiding relation and in circuit with said means for periodically opening the primary winding circuit, and a secondary winding on said core structure overlapping said primary winding and having a substantially greater number of turns, each of the turns of said primary winding extending in width across substantially all the turns of said secondary winding.

2. In an internal combustion engine magneto construction of the type having relatively rotatable core and magnetic field structures with an air gap therebetween, a bracket adapted to be mounted on an internal combustion engine, a magnetic core carried by said bracket, a

pole on said core, a magneto coil assembly on said pole comprising primary and secondary windings, said primary winding having :a pair of capaoitatively related conductors wound in the same sense on said pole and connected in series aiding relation, a wire Wound secondary Winding surrounding said primary Winding, each of the turns of said primary Winding extending in Width across substantially all the turns of said secondary winding, a housing on said bracket, a pair of breaker points disposed Within said housing, said breaker points being connected in series with said primary Winding, and means responsive to engine rotation for intermittently opening and closing the breaker points, each turn of said primary Winding having a portion closely adjacent said air gap.

3. In 'a genenator-magneto construction, a stationary core structure, a rotatable magnetic field structure carrying a magnet, a plurality of poles on said core structure having generator windings thereon, a magneto pole on said core structure coacting with said magnetic field structore through an air gap, a primary magneto Winding on said magneto pole comprising a pair of electrically conductive flat strips: Wound in overlapping relation on said pole, insulative material between said electrically conductive strips, each tom of said primary Winding having U a portion closely adjacent the air gap between said field structure and magneto pole, means connecting said strips in series aiding relation in a closed circuit, a pair of breaker points in said circuit, a cam connected to said rotatable magnetic field structure for intermittently opening and closing said breaker points, and a Wire wound secondary winding surrounding said primary winding and having a substantially greater number of turns, each of the turns of said primary winding extending in width across substantially all the turns of said secondary winding.

References Cited in the file of this patent UNITED STATES PATENTS 1,460,390 OLeary July 3, 1923 2,446,761 Harmon Aug. 10, 1948 2,461,233 Schaevitz Feb. 8, 1949 2,521,513 Gray Sept. 5, 1950 2,710,929 Phelon June 14, 1955' FOREIGN PATENTS 293,758 Germany Aug. 28, 1916 465,619 Great Britain May 11, 1937 575,115 Great Britain Feb. 4, 1946 590,101 Great Britain July 8, 1947 

1. IN AN IGNITION COIL FOR USE IN A MAGNETO ASSEMBLY OF THE TYPE HAVING RELATIVELY ROTATABLE CORE AND MAGNETIC FIELD STRUCTURES WITH AN AIR GAP THEREBETWEEN AND MEANS FOR PERIODICALLY OPENING A PRIMARY WINDING CIRCUIT, A PRIMARY WINDING COMPRISING AT LEAST TWO ELONGATED FLAT STRIPS OF ELECTRICALLY CONDUCTIVE MATERIAL WOUND IN OVERLAPPING RELATION ON A PORTION OF SAID CORE STRUCTURE, DIELECTRIC MATERIAL SEPARATING SAID STRIPS, EACH TURN OF SAID PRIMARY WINDING AND HAVING A PORTION POSITIONABLE CLOSELY ADJACENT SAID AIR GAP, MEANS CONNECTING SAID STRIPS IN SERIES AIDING RELATION AND IN CIRCUIT WITH SAID MEANS FOR PERIODICALLY OPENING THE PRIMARY WINDING CIRCUIT, AND A SECONDARY WINDING ON SAID CORE STRUCTURE OVERLAPPING SAID PRIMARY WINDING AND HAVING A SUBSTANTIALLY GREATER NUMBER OF TURNS, EACH OF THE TURNS OF SAID PRIMARY WINDING EXTENDING IN WIDTH ACROSS SUBSTANTIALLY ALL THE TURNS OF SAID SECONDARY WINDING. 